1. Field of the Invention
The present invention generally relates to a magnetic disk apparatus, and more particularly to a magnetic disk apparatus which controls a protruding amount of a magnetic head element having a read element and a write element by means of a heater provided in the magnetic head element.
2. Description of the Related Art
In a magnetic disk apparatus, it is necessary to control the distance (magnetic spacing) between the magnetic head element and a magnetic disk. A magnetic disk apparatus that controls the magnetic spacing by using the heat of a heater is known (see Japanese Patent Laid-Open No. 2003-297029).
This magnetic spacing control is generally carried out in the following manner. That is, a heater is provided in the magnetic head element or the vicinity thereof. The heater generates heat by the supply of power thereto. As a result of this heat, the magnetic head element undergoes thermal expansion to protrude in the direction of a magnetic disk that is disposed facing the magnetic head element. At this time, depending on the shape of the magnetic head element, the surface facing the magnetic disk appears as though it is protruding as the result of the entire magnetic head element being deformed (see Japanese Patent Laid-Open No. 2003-297029), or the surface facing the magnetic disk simply appears to have protruded. The amount of protrusion of the magnetic head element in the direction of the magnetic disk (hereunder, referred to as “protruding amount”) is controlled by the amount of power supplied to the heater, and thus the magnetic spacing is controlled.
When power is supplied to the heater to control the protruding amount, the heater generates heats to increase the temperature of the magnetic head element (and the region in the vicinity thereof). This is a fundamental operation in a magnetic disk apparatus equipped with this kind of magnetic head element having a heater for controlling a protruding amount (hereunder, referred to simply as “magnetic head element with a heater”), and can not be avoided.
However, increasing the temperature of the magnetic head element causes a decrease in the reliability of the magnetic head element. For example, with respect to the write element of the magnetic head element, when processing to write data onto a magnetic disk is continuously performed in a high temperature state it causes a failure such as migration or a disconnection in the write coil. With respect to the read element of the magnetic head element, the passage of a sense current over a long period in a high temperature environment leads to the occurrence of migrations in the read element or noise or the like is produced due to instability in the read element in a high temperature state. It is therefore necessary to use the magnetic head element in a temperature region that does not damage the reliability of the magnetic head element.